1. BASICS OF WAVEFORM INTERPRETATION Michael Haines, MPH, RRT-NPS, AE-C

2. Objectives
Identify graphic display options provided by mechanical ventilators.
Describe how to use graphics to
more appropriately adjust the patient ventilator interface.

3. Monitoring and analysis of graphic display of curves and loops during mechanical ventilation has become a useful and popular way to determine not only how patient are being ventilated but also a way to assess problems occurring during ventilation.

4. Uses of Flow, Volume, and Pressure Graphic Display
Confirm mode functions
Detect auto-PEEP
Determine P-V synchrony
Assess and adjust trigger levels
Measure the work of breathing
Adjust tidal volume and minimize overdistension
Assess the effect of bronchodilator administration
Detect equipment malfunctions
Determine appropriate PEEP level

5. Uses of Flow, Volume, and Pressure Graphic Display
Evaluate adequacy of inspiratory time in pressure control ventilation
Detect the presence and rate of continuous leaks
Assess inspiratory termination criteria during Pressure Support Ventilation
Determine appropriate Rise Time

6. The graphic display of flow, pressure and volume is generally visualized in two formats:
Waveforms
Loops

7. Most Commonly used Waveforms
Pressure vs. Time
Flow vs. Time
Volume vs. Time

8. Pressure vs. Time Curve Paw cmH2O 1 2 3 4 5 6 30 A B C PIP Baseline
Sec
Paw
cmH2O A B C
PIP
Baseline
Mean Airway Pressure
-10

9. Pressure-Time Curve Paw Volume Ventilation Pressure Ventilation20
Volume Ventilation
Pressure Ventilation
Paw
Expiration
cmH2O
Sec 1 2 3 4 5 6

10. PIP: compliance resistance volume flow
PEEP
Pressure
PEEP
time

11. PIP Pplat PEEP resistance flow compliance tidal volume
No active breathing
Treats lung as single unit
PIP
resistance
flow
Pplat
end-inspiratory
alveolar pressure
compliance
tidal volume
PEEP

12. Work to Trigger 30
Paw
cmH2O
Sec 1 2 3 4 5 6
-10

13. Adequate Flow During Volume-Control Ventilation30
Adequate flow P aw
cmH2O
Time (s) 1 2 3
-10

14. Inadequate Flow During Volume-Control Ventilation30
Flow set too low
Adequate flow P aw
cmH2O
Time (s) 1 2 3
-10

15. Patient/Ventilator Synchrony Volume Ventilator Delivering a Preset Flow and Volume
Adequate Flow
Paw
Sec
cmH2O 1 2 3 4 5 6
-20

16. Patient/Ventilator Synchrony The Patient Outbreathing the Set Flow
Air Starvation
Paw
Sec
cmH2O 1 2 3 4 5 6
-20

17. Plateau Time Paw Inadequate plateau time cmH2O 30 1 2 3 4 5 6 -20 SEC
A good way to identify an adequate plateau time is to observe the pressure-time curve. This slide shows an inadequate plateau time; no plateau has occurred. This could lead to an inaccurate estimation of plateau pressure.
SEC
cmH2O 1 2 3 4 5 6
-20

18. Plateau Time Paw Adequate Plateau Time cmH2O 30 1 2 3 4 5 6 -20 SEC
Here, we see that a plateau has occurred, as evidenced by the flattening of the pressure curve at the arrow.
SEC
cmH2O 1 2 3 4 5 6
-20

19. . Flow vs.Time Curve V Inspiration 120 1 2 3 4 5 6 120 INSP SEC LPM
EXH
120

20. . Flow vs.Time Curve V Inspiration Expiration 120 1 2 3 4 5 6 120 INSP
SEC
LPM 1 2 3 4 5 6
Expiration
EXH
120

21. . Flow vs.Time Curve V Constant Flow Descending Ramp Inspiration 120 1
SEC
LPM 1 2 3 4 5 6
EXH
120

22. . Flow-Time Curve V Insp. Pause Expiration 120 1 2 3 4 5 6 120 INSP
SEC
LPM 1 2 3 4 5 6
Expiration
EXH
120

23. Inspiratory Time Short Normal Long

24. Expiratory Flow Rate and Changes in Expiratory Resistance
120 .
SEC V
LPM 1 2 3 4 5 6
This slide depicts a long expiratory phase. Note the low expiratory flow rate and extended exhalation phase. This could be caused by a number of clinical situations: bronchospasm, COPD, expiratory filter contamination, secretions or water in the tubing. Watching for changes in expiratory flow helps judge the efficacy of any intervention.
-120

25. 120 .
SEC V
LPM 1 2 3 4 5 6
A higher expiratory flow rate and a decreased expiratory time denote a lower expiratory resistance. A decrease in expiratory resistance may also be observed after the patient receives a bronchodilator (e.g. MDI or aerosolized neb tx). Monitoring the duration of the therapy’s effect can help determine the indicated frequency of therapy.
120

26. Obstructed Lung
Delayed flow return

27. . Combined Screens Paw V Volume Ventilation cmH2O 20 1 2 3 4 5 6 Sec
As you remember from our discussion of flow curves, both square and decelerating flow patterns are used clinically. Each creates a differently shaped pressure curve. Let’s start out with the pressure pattern created by the square waveform of volume ventilation. At the beginning of inspiration, seen here in green, pressure increases in a linear fashion due to the constant flow of the square flow waveform pattern. 1 2 3 4 5 6 . V

28. Pressure-Time and Flow-Time Curves20
Volume Ventilation
Paw
Expiration
cmH2O
Sec
Exhalation, seen here in yellow, occurs when the tidal volume has been delivered or the high pressure limit has been reached. Flow ceases and exhalation begins. This is a passive process caused by the elastic recoil of the lung. 1 2 3 4 5 6 . V

29. Pressure-Time and Flow-Time Curves Different Inspiratory Flow Patterns20
Volume Ventilation
Paw
Expiration
Inspiration
cmH2O
Sec
Let’s take a look at the pressure curve resulting from a volume-based breath with a decelerating flow pattern. As you can see in green here, pressure increases more rapidly from the PEEP level when the decelerating flow curve is used. This pressure curve is starting to look more like a pressure-based breath. 1 2 3 4 5 6 . V

30. Pressure-Time and Flow-Time Curves20
Pressure Ventilation
Volume Ventilation
Inspiratory Time
Paw
cmH2O
In pressure-based ventilation, once the Pinsp has been reached, the pressure then remains constant for the Tinsp set on the ventilator. Flow decelerates towards end inspiration and then remains at or near zero base line until the set inspiratory time is met. Note the pressure curves are similar. The difference is in the ventilators response to changes in resistance, compliance, or patient demand.
Sec 1 2 3 4 5 6 . V

31. How quickly inspiratory flow accelerates to achieve set pressure.
Rise Time Inspiratoty Rise Time Percentage Flow Acceleration Percentage
How quickly inspiratory flow accelerates to achieve set pressure.

32. Flow Acceleration Percent Rise Time
Minimal Pressure Overshoot P
Slow rise Moderate rise Fast rise
Did anybody say rise time or flow acceleration percent? Literature suggests that inappropriate flow rate, too high or too low at any time during the inspiratory phase in PCV or PSV, may result in increased inspiratory muscle effort or work of breathing. It can also increase the likelihood of patient discomfort and patient/ventilator asynchrony. FAP allows the clinician to sculpt the shape of the rise to pressure to meet patient demand or comfort. Slow, moderate, and aggressive rise to pressure curves are shown. What is happening at the two arrows?
On the pressure-time curve, it is a minimal pressure overshoot caused by an aggressive rise to pressure. On the flow curve, it is a pressure relief that occurs with an active exhalation valve. What happens when there isn’t an active exhalation valve? . V
Pressure Relief
Time

33. Patient / Ventilator Synchrony Volume Ventilation Delivering a Preset Flow and Volume30
Adequate Flow
Paw
Sec
All right, now let’s get on with the fun stuff: detecting abnormalities on waveforms. When your patient begins to fight the ventilator and becomes asynchronous, your job as a clinician is to determine why. We all know that many things can cause the patient to become out of synch. It could be caused by pain, frustration from trying to communicate, or their spouse may have just told them they are filing for divorce. But on a more serious note, patient ventilator dysychrony can be caused when the patient outstrips the peak flow set on the ventilator. Let’s take a look at this.
This is a normal pressure curve in volume ventilation with an adequate setting for peak flow.
cmH2O 1 2 3 4 5 6
-20

34. Patient / Ventilator Synchrony The Patient Is Outbreathing the Set Flow30
Air Starvation
Paw
Sec
What we see here is a patient’s inspiratory flow demand greater than the peak flow set on the ventilator, which can lead to patient/ventilator dysynchrony. What are we going to do to amend this situation?
cmH2O 1 2 3 4 5 6
What options do we have?
-20

35. We Can Switch to a Decelerating Flow Pattern: More Flow Up Front
120 . V
SEC
LPM 1 2 3 4 5 6
We could increase peak flow, but that would increase peak pressure; or we could switch to a decelerating flow pattern which would put more flow up front and perhaps satisfy the patient’s inspiratory flow needs.
-120

36. If Peak Flow Remains the Same, I-Time Increases: Could Cause Asynchrony
120 . V
SEC
LPM 1 2 3 4 5 6
However, remember what we talked about earlier. If the peak flow is left at the same setting when we switch to a decelerating flow pattern, the inspiratory time will increase. A decreased expiratory time may have the potential to cause patient/ventilator dysynchrony in and of itself. Perhaps a different mode of ventilatory support may be more appropriate, such as PCV or PS.
-120

37. Changing Flow Waveform in Volume Ventilation: Effect on Inspiratory Time
120 . V
SEC
LPM 1 2 3 4 5 6
As we discussed earlier, both square and decelerating flow patterns are commonly used in clinical practice. We will not debate the clinical application of these flow patterns, but will point out the impact of changing from a square to decelerating flow curve in volume ventilation without changing the set peak flow. Note the increase in inspiratory time with the decelerating flow pattern.
-120

38. Increased Peak Flow: Decreased Inspiratory Time
120 . V
SEC
LPM 1 2 3 4 5 6
If the goal is to maintain a similar inspiratory time, this can be accomplished by increasing peak flow to approximate the same inspiratory time with the decelerating flow pattern that existed with the square wave pattern. This could decrease the potential for developing Auto-PEEP.
-120

39. Detecting Auto-PEEP
120 . V
SEC
LPM 1 2 3 4 5 6
We can look at our flow-time curve. If there is zero flow at the end of exhalation, it would indicate an equilibration of the lung and circuit pressure.
Note: There can still be pressure in the lungs behind airways that are completely obstructed.
Zero flow at end exhalation indicates equilibration of lung and circuit pressure
-120
Note: There can still be pressure in the lung behind airways that are completely obstructed

40. Detecting Auto-PEEP
120 . V
SEC
LPM 1 2 3 4 5 6
On the other hand, if the transition from exhalation to inspiration occurs without the expiratory flow returning to zero, you have Auto-PEEP present.
The transition from expiratory to inspiratory occurs without the expiratory flow returning to zero
120

41. Flow Waveform
flow
inhalation
time
auto-PEEP
exhalation

42. Auto-PEEP should be measured with set PEEP = 0
sensitivity
-1 cm H2O
auto-PEEP
10 cm H2O
trigger effort = 11 cm H2O
3 cm H2O
trigger effort = 4 cm H2O
PEEP
7 cm H2O
Auto-PEEP should be measured with set PEEP = 0

43. Volume vs.Time Curve Inspiration VT 800 ml 2 3 4 5 6 1 SEC
The volume-time curve shows the gradual changes in the volume that is delivered during inspiration. Volume is typically measured in milliliters. Pictured in green is the inspiratory phase, in which volume increases continuously until the set tidal volume is achieved or the high pressure alarm limit has been reached, or I-Time has expired.

44. Volume vs.Time Curve Expiration VT 800 ml 1 2 3 4 5 6 SEC
During expiration, seen in yellow here, the transferred volume decreases, again due to the passive recoil of the lung. Generally, what goes in comes out, unless you have a leak in the patient circuit or the patient, or gas is trapped in the lung. 1 2 3 4 5 6

45. Typical Volume Curve I-Time E-Time 1.2 A B VT Liters 1 2 3 4 5 6 -0.4
SEC 1 2 3 4 5 6
-0.4
A = inspiratory volume
B = expiratory volume

46. Air Trapping or Leaks 1.2 A VT Liters 1 2 3 4 5 6 -0.4
SEC 1 2 3 4 5 6
-0.4
A = exhalation that does not return to zero

47. Loops
Pressure-Volume Loops
Flow-Volume Loops

48. Pressure-Volume Loop Paw VT 20 40 60 -60 0.2 0.4 0.6 cmH2O LITERS20 40 60
-60
0.2
LITERS
0.4
0.6
Paw
cmH2O VT
We have reviewed the normal components of the three standard time curves: Flow, Pressure, and Volume. Now, let’s investigate the normal components of the pressure-volume loop. Instead of plotting one parameter against time, the pressure-volume loop plots the interaction between pressure, on the horizontal axis, and volume, on the vertical axis.

49. Mandatory Breath Paw Inspiration VT 20 40 60 -60 0.2 0.4 0.6 cmH2O20 40 60
-60
0.2
LITERS
0.4
0.6
Paw
cmH2O VT
On a ventilator-initiated mandatory breath, or VIM, the movement of the PV Loop is counterclockwise, starting with inspiration, shown here in green. During inspiration, the lung begins to fill and normally there is a simultaneous increase in both pressure and volume.

50. Mandatory Breath Counterclockwise Paw Expiration Inspiration VT 0.6
LITERS
0.6
Expiration
0.4
Inspiration
0.2
When the inspiration criteria are met, exhalation begins as pictured in yellow here. Normally, this curve resembles a football.
Paw
cmH2O
-60 40 20 20 40 60

51. Spontaneous Breath Paw Inspiration VT Clockwise 0.6 0.4 0.2 cmH2O -60
LITERS
0.6
0.4
Inspiration
0.2
During a spontaneous, non-pressure-supported breath, the rotation is clockwise; inspiration and then expiration.
Paw
cmH2O
-60 40 20 20 40 60

52. Spontaneous Breath Paw Inspiration Expiration VT Clockwise 0.6 0.4 0.2
LITERS
0.6
0.4
Inspiration
Expiration
0.2
During a spontaneous, non-pressure-supported breath, the rotation is clockwise; inspiration and then expiration.
Paw
cmH2O
-60 40 20 20 40 60

53. Work of Breathing Paw VT 0.6 0.4 0.2 -60 -40 -20 20 40 60 cmH2O LITERS
The arrow indicates patient work of breathing. Inspiratory effort to the left of the vertical axis translates into increased inspiratory workload for the patient. This is commonly addressed by instituting flow triggering.
Paw
-60
-40
-20 20 40 60
cmH2O

54. Assisted Breath Paw Assisted Breath VT 0.6 0.4 0.2 cmH2O -60 40 20 20
LITERS
0.6
0.4
Assisted Breath
0.2
When a patient-initiated mandatory (PIM) breath is triggered, you will initially see a clockwise rotation like a spontaneous breath; then the ventilator takes over and delivers the mandatory breath. At the point marked with the white arrow, it changes to the classic counterclockwise rotation seen with a VIM breath.
Paw
cmH2O
-60 40 20 20 40 60

55. Assisted Breath Paw Assisted Breath Inspiration VT 0.6 0.4 0.2 cmH2O
LITERS
0.6
0.4
Assisted Breath
0.2
Inspiration
When a patient-initiated mandatory (PIM) breath is triggered, you will initially see a clockwise rotation like a spontaneous breath; then the ventilator takes over and delivers the mandatory breath. At the point marked with the white arrow, it changes to the classic counterclockwise rotation seen with a VIM breath.
Paw
cmH2O
-60 40 20 20 40 60

56. Assisted Breath Paw Expiration Assisted Breath Inspiration VT
Clockwise to Counterclockwise
LITERS
0.6
Expiration
0.4
Assisted Breath
0.2
Inspiration
When a patient-initiated mandatory (PIM) breath is triggered, you will initially see a clockwise rotation like a spontaneous breath; then the ventilator takes over and delivers the mandatory breath. At the point marked with the white arrow, it changes to the classic counterclockwise rotation seen with a VIM breath.
Paw
cmH2O
-60 40 20 20 40 60

57. Pressure-Volume Loop ChangesVT
LITERS
0.6
0.4
0.2
The pressure-volume loop changes, flattening out and moving to the right. What could cause this to happen?
Paw
-60
-40
-20 20 40 60
cmH2O

58. Changes in Compliances
Indicates a drop in compliance (higher pressure for the same volume) VT
LITERS
0.6
0.4
0.2
Did anybody say decrease in compliance? The difference between the white arrow and the red arrow represents a change in compliance as indicated by an increase in pressure without a corresponding increase in tidal volume.
Paw
-60 40 20 20 40 60
cmH2O

59. Lung Overdistension

60. Overdistension Paw A = inspiratory pressure B = upper inflection pointVT
A = inspiratory pressure
B = upper inflection point
C = lower inflection point
LITERS
0.6 A
0.4 B
0.2
Overdistention is caused by a combination of PEEP and too much volume or pressure. A is the peak inspiratory pressure; B is the upper inflection point; C is the lower inflection point. The lower inflection point identifies the level of PEEP where the lung is more compliant. This is also referred to as critical opening pressure. The upper inflection point indicates where the lung becomes less compliant and illustrates where overdistension starts to occur. Decreasing the volume or pressure may help avoid barotrauma in this situation. C
Paw
-60
-40
-20 20 40 60
cmH2O

61. Pressure – Volume Loops

62. Pressure – Volume Loops

63. Pressure – Volume Loops

64. Flow -Volume Loops Volume Control
Tidal Volume
Flow
Inspiration
Volume
Expiration

65. Flow -Volume Loops Volume Control
Tidal Volume
Peak Inspiratory Flow
Peak Expiratory Flow
Flow
Inspiration
Volume
Expiration

66. ETT or Circuit Leaks

67. Obstructive Pattern

68. Bronchodilator Response
BEFORE 3 2 1 . . V
LPS V
LPS
This example shows before and after flow-volume loops that indicate a response to bronchodilators. The loop at the far left (before) is the control. Compare the three peak expiratory flow rates and the lower half of each loop. In the center loop, the relatively low expiratory flow rate (A) and the scalloped shape (B) near end exhalation indicates a negative response to treatment. At the far right, the higher expiratory flow rate and the flatter shape near end exhalation indicate a positive response. 1 2 3

69. Bronchodilator Response
BEFORE
AFTER
Worse 3 3 2 2 1 1 . . V
LPS V
LPS
This example shows before and after flow-volume loops that indicate a response to bronchodilators. The loop at the far left (before) is the control. Compare the three peak expiratory flow rates and the lower half of each loop. In the center loop, the relatively low expiratory flow rate (A) and the scalloped shape (B) near end exhalation indicates a negative response to treatment. At the far right, the higher expiratory flow rate and the flatter shape near end exhalation indicate a positive response. 1 1 2 2 3 3

70. Bronchodilator Response
BEFORE
AFTER
Worse
Better 3 3 2 1 3 V
LPS .
INSP 2 2 1 1 . . V
LPS V
LPS VT
This example shows before and after flow-volume loops that indicate a response to bronchodilators. The loop at the far left (before) is the control. Compare the three peak expiratory flow rates and the lower half of each loop. In the center loop, the relatively low expiratory flow rate (A) and the scalloped shape (B) near end exhalation indicates a negative response to treatment. At the far right, the higher expiratory flow rate and the flatter shape near end exhalation indicate a positive response. 1 1 2 2 3 3
EXH

71. What Mode is This?

72. What Mode is This?

73. What Mode is This?

74. What Mode is This?

75. Remember
Waveforms and loops are graphical representation of the data collected by the ventilator.
Typical Tracings
Pressure-time,
Flow-time,
Volume -time
Loops
Pressure-Volume
Flow-Volume
Assessment of pressure, flow and volume waveforms is a key aspect in the management of the mechanically ventilated patient.

76. The End!